1. Field of the Invention
The invention relates to a process for the production of coherent monochromatic radiation (laser light), the frequency of which can be changed, by means of a dyestuff laser which consists of a reservoir for the dyestuff solution and an energy source, associated therewith, which is capable of exciting the dyestuff solution to produce an emission, the radiation produced being in the wavelength range of 420 to 480 nm.
2. Discussion of Prior Art
A laser is a light amplification device by means of which it is possible to produce coherent monochromatic light of a high spectral and geometric intensity density. The laser consists of an optical resonator which contains the liquid laser-active material in a thin-walled quartz cell. The cell is usually part of a closed system through which the dyestuff solution is circulated by pumping whilst the laser is in operation. The active medium can also be in the form of a liquid jet, which issues from a nozzle perpendicular to the optical axis and transverses the resonator. Local overheating, which would lead to optical inhomogeneities, is avoided in both arrangements.
The excitation of the dyestuffs is effected with the aid of energy sources, by means of electrons or light, and the dyestuff laser can also be excited by a gas laser, for example a nitrogen laser, argon laser or krypton laser.
The excitation, which is also termed optical pumping, has the effect of raising the electrons of the molecule of the laser dyestuff from their normal state to a higher energy state, from which a radiation transition takes place. If the number of molecules in the excited state exceeds that of the molecules in lower states, this gives rise to stimulated transitions, by means of which the light is amplified in the optical resonator.
If one of the laser mirrors is partically transparent to light, a part of the radiation leaves the apparatus in the form of a laser beam. Dyestuffs which can be excited particularly easily exhibit the phenomenon of "super radiance" with highly effective excitation. This can be observed, for example, if a quartz cell containing the solution of such a dyestuff is placed in the beam of a nitrogen laser. The solution then emits light in a preferred direction, similarly to the case of a laser, without being located between resonator mirrors.
A considerable advantage of the dyestuff laser compared with a solid laser or gas laser is its ability to supply laser radiation of a frequency which can be changed. Because of the width of the fluorescence band of the dyestuffs employed, dyestuff lasers can be so tuned, by inserting a frequency-selective element, for example a reflection grating, prism or doubly refracting filter, that laser light is emitted at any desired wavelength within the entire flourescence band of the dyestuff.
Although a large number of suitable dyestuffs have already been proposed, there is, nevertheless, still a considerable lack, in many regions of the visible wavelength range, of compounds which give a very high degree of effectiveness of the laser.